Overheating too much!

I'm having a lot of problems lately so I'll try to make it as short as I can.
(I have mazda mx-3, engine: 1.8v6, year:1992). Sorry for english,not my native language
1- after changing water pump and thermostat, my car boils up. It happens all the time and I can't figure out why.
About half year ago my engine boiled up quite a lot(it was a hot summer). It seemed that water pump was dead. I changed it and had to repair the heads(they were screwed). After repairs everything seemed normal
Now the coolant is simply dissapearing somewhere and I can't understand why and where. I have- changed another water pump and another thermostat- nothing at all. Still boils like hell. What I have noticed- my fan is not turning on at all!
I've been repairing this car for eternity and I'm sick and tired of all those little things that simply can't be repaired!(I repair my car @ service shop, since I don't have garage of my own).
I suspect 2 things- air in the system(maybe the head is faulty) or something else? Why all my coolant is gone? (picked up the car, can't see any trace of coolant anywhere). Car runs fine,no white smoke(as it should be,if coolant would get into engine). Any help please? :?

I have the same problem with my car overheating and water magically vanishing, I have found that the pipe connectors that go into the bulkhead are leaking under pressure when the engine gets hot, they get to a certain point then it blows it out the back, these are mazda only parts unfortunately and very hard to notice as the water runs down the back of the engine and the heat from exhausts etc there dries it very quikcly

next watch your temp guage and it should kick in just over halfway, I have found a broken wire in the plug connector for the fan in mine and have now cut the plug out and used bullet connectors and its all fine now, another route to try is adding a second fan

if you disconnect the plug and wire the fan direct to battery, if it works its not the fan, you need to run the engine until hot then connect the other side of the plug to a voltage meter and make sure its getting voltage, if no voltage it maybe the the sensor for the fan _ look at top of engine where you fill the engine up and next to it is 2 sensors - one for ecu and gauage the other fires the fan at a certain temp, make sure its connected and connections are fine otherwise it needs replacing

Other thing to try is make sure water is not coming out of cap, engine will boil over if the cap doesnt hold pressure, the water system needs pressure as the boiling temperature goes up when the water is pressurised so water will boil at 110 degress under 1 bar so check the cap too

Other thing to try is make sure water is not coming out of cap, engine will boil over if the cap doesnt hold pressure, the water system needs pressure as the boiling temperature goes up when the water is pressurised so water will boil at 110 degress under 1 bar so check the cap too

about the caps- is there any way to find out do they hold the pressure? I know that pressure in cooling system is ~0.9bar, but if there is to much pressure, it would be driven out to coolant reservouar. But the radiator simply sucks out the coolant from that expandable reservouar.
There is no oil in the expansion reservouar either so I guess I'll go with the clamps and tubing stuff,before I proceed further. If there is anything at all, don't hesitate and write coz I'm really out of options right now but I need my car up and running until sunday.

It seems that I have faulty head or radiator, because there is no end to air bubbles :(.
Replaced radiator and engine coolant caps- nothing happend.
Thermostat simply won't open,maybe that's one more problem to solve :( …

make your own leak test:
Get a bicycle tube, clamp it to one end of the radiator, block off the other end with another part of the tube. Attach air compressor, put under water, observe bubbles or listen for hissing.

If you have already done the basics and checked for oil and water mixing, and checked that the rad caps are sealing properly.

1) First off fix your fan
Check fuse, Check wires and plugs, test fan motor, check temp sensor.
That might fix it if not see below.

2) Is the thermostat working?
Check if the pipes going to the radiator are getting hot. Let the car get up to temp and feel both hoses if they get hot then the thermostat is ok. If they stay cold take out the thermostat and see if that fixes it.

3) Blocked radiator / air (not water) leak on two main coolant hoses
Take off the radiator turn it upside down and flush it out using a hose pipe, block off the holes with your hand fill it with water and give it a good shake, then flush again with a hose in both directions. Clean up the ends of the rubber pipes and where they go onto. Throw away the crap hose clips and replace with jubilee clips.

While the rad is out inspect it for leaks, any blue stains on it? obvious leaks? pressure test it if you can.

4) Blocked heater matrix / Air leak on hoses
Undo both heater hoses from the engine side not the bulkhead and put a hose pipe up one and flush it out, put your thumb over the other side to fill it up then take it off and let water run out. Then repeat for the second hose. Take the hoses off completely clean up all the ends and connections, throw away the clips and replace with decent jubilee clips.

5) Flush the block
Its very rarely a cause of problems unless you have had a head gasket go really badly in the past in the past and not flushed it before repair. To flush you need to undo the end of the coolant hose that goes to the thermostat, then remove the thermostat, lift the hose up higher than the engine and then put a hose pipe down it. Then undo the bottom radiator hose and put the hose pipe down where the thermostat was. Do it until it runs clear.

6) What next?
Well thats all the easy overheating culprits, blockages and leaks ruled out, so if these havent sorted it then its either a head gasket or cracked head.

You need to do a cylinder leakage test and compression test to tell for certain if your heads gone with an air and water mix.

There is a good chance that your fan went out ages ago and that caused it to overheat which was what caused your head to go last time, then you fixed the head but not the fan and so it just overheated again and blew the head again. If the head is gone again make sure you get it skimmed and pressure tested whilst hot.

I bought a car once with the seller telling me that the head was gone and beyond repair as it kept going, 3 people had bought the car and tried to fix it and given up.

It took me 20 mins to spot it, just had to throw away the old rusty coolant hose clips and replace with jubilee clips and problem solved.

To DJ: I can't remember 100% on the MX-3 but on alot of cars you can simply do away with those plastic hose ends going into the bulkhead. Just brake them off and connect straight to the pipe. Most of the time they are just there for a quick release solution. Just bin them and use jubilee clips.